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Bit slicing is a technique for constructing a
processor Processor may refer to: Computing Hardware * Processor (computing) **Central processing unit (CPU), the hardware within a computer that executes a program *** Microprocessor, a central processing unit contained on a single integrated circuit (I ...
from modules of processors of smaller bit width, for the purpose of increasing the word length; in theory to make an arbitrary ''n''-bit
central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...
(CPU). Each of these component modules processes one bit field or "slice" of an
operand In mathematics, an operand is the object of a mathematical operation, i.e., it is the object or quantity that is operated on. Example The following arithmetic expression shows an example of operators and operands: :3 + 6 = 9 In the above examp ...
. The grouped processing components would then have the capability to process the chosen full word-length of a given software design. Bit slicing more or less died out due to the advent of the
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
. Recently it has been used in
arithmetic logic unit In computing, an arithmetic logic unit (ALU) is a Combinational logic, combinational digital circuit that performs arithmetic and bitwise operations on integer binary numbers. This is in contrast to a floating-point unit (FPU), which operates on ...
s (ALUs) for
quantum computer Quantum computing is a type of computation whose operations can harness the phenomena of quantum mechanics, such as superposition, interference, and entanglement. Devices that perform quantum computations are known as quantum computers. Though ...
s and as a software technique, e.g. for
cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...
in
x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was introd ...
CPUs.


Operational details

Bit-slice processors (BSPs) usually include 1-, 2-, 4-, 8- or
16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...
arithmetic logic unit In computing, an arithmetic logic unit (ALU) is a Combinational logic, combinational digital circuit that performs arithmetic and bitwise operations on integer binary numbers. This is in contrast to a floating-point unit (FPU), which operates on ...
(ALU) and control lines (including carry or overflow signals that are internal to the processor in non-bitsliced
CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...
designs). For example, two 4-bit ALU chips could be arranged side by side, with control lines between them, to form an 8-bit ALU (result need not be power of two, e.g. three 1-bit units can make a 3-bit ALU, thus 3-bit (or ''n''-bit) CPU, while 3-bit, or any CPU with higher odd number of bits, hasn't been manufactured and sold in volume). Four 4-bit ALU chips could be used to build a 16-bit ALU. It would take eight chips to build a 32-bit word ALU. The designer could add as many slices as required to manipulate longer word lengths. A
microsequencer In computer architecture and engineering, a sequencer or microsequencer generates the addresses used to step through the microprogram of a control store. It is used as a part of the control unit of a CPU or as a stand-alone generator for address ...
or
control ROM Control may refer to: Basic meanings Economics and business * Control (management), an element of management * Control, an element of management accounting * Comptroller (or controller), a senior financial officer in an organization * Controllin ...
would be used to execute logic to provide data and control signals to regulate function of the component ALUs. Known bit-slice microprocessors: * 2-bit slice: **
Intel 3000 This generational list of Intel processors attempts to present all of Intel's processors from the pioneering 4-bit 4004 (1971) to the present high-end offerings. Concise technical data is given for each product. Latest 13th generation Cor ...
family (1974, now discontinued), e.g. Intel 3002 with Intel 3001, second-sourced by Signetics and
Intersil Intersil is an American semiconductor company headquartered in Milpitas, California. As of February 24, 2017, Intersil is a subsidiary of Renesas. The previous Intersil was formed in August 1999 through the acquisition of the semiconductor busin ...
** Signetics
8X02 8X or 8-X may refer to: *8x, or eight times in multiplication *8X, code name for Enhanced Imaging System *8X, abbreviation for Octuple scull * Precorrin-8X methylmutase * South African Class 8X 2-8-0 locomotive *8X Bayshore; see List of San Fr ...
family (1977, now discontinued) * 4-bit slice: **
National National may refer to: Common uses * Nation or country ** Nationality – a ''national'' is a person who is subject to a nation, regardless of whether the person has full rights as a citizen Places in the United States * National, Maryland, ce ...
IMP family, consisting primarily of the IMP-00A/520 RALU (also known as MM5750) and various masked ROM microcode and control chips (CROMs, also known as MM5751) *** National GPC/P / IMP-4 (1973), second-sourced by Rockwell *** National IMP-8, an 8-bit processor based on the IMP chipset, using two RALU chips and one CROM chip *** National IMP-16, a 16-bit processor based on the IMP chipset, e.g. four RALU chips with one each IMP16A/521D and IMP16A/522D CROM chips (additional optional CROM chips could provide instruction set additionis) **
AMD Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufactur ...
Am2900 Am2900 is a family of integrated circuits (ICs) created in 1975 by Advanced Micro Devices (AMD). They were constructed with bipolar devices, in a bit-slice topology, and were designed to be used as modular components each representing a different ...
family (1975), e.g. AM2901, AM2901A, AM2903 **
Monolithic Memories Monolithic Memories, Inc. (MMI) produced bipolar PROMs, programmable logic devices, and logic circuits (including 7400 series TTL). A team of MMI engineers, under the direction of Ze'ev Drori and headed by John Birkner and H. T. Chua, invente ...
5700/6700 family (1974) e.g. MMI 5701 / MMI 6701, second-sourced by
ITT Semiconductors ITT Inc., formerly ITT Corporation, is an American worldwide manufacturing company based in Stamford, Connecticut. The company produces specialty components for the aerospace, transportation, energy and industrial markets. ITT's three businesse ...
**
Texas Instruments SBP0400 The Texas Instruments SBP0400 (SBP = silicon bipolar), also known as SBC 0400 and X0400, is a microprogrammable 4-bit slice processor that was introduced in 1976 (delivery began in December 1975). It was one of the first LSI processors and was ...
(1975) and SBP0401, cascadable up to 16 bits ** Texas Instruments SN74181 (1970) ** Texas Instruments SN74S281 with SN74S282 ** Texas Instruments SN74S481 with SN74S482 (1976) **
Fairchild Fairchild may refer to: Organizations * Fairchild Aerial Surveys, operated in cooperation with a subsidiary of Fairey Aviation Company * Fairchild Camera and Instrument * List of Sherman Fairchild companies, "Fairchild" companies * Fairchild Fash ...
33705 ** Fairchild 9400 (MACROLOGIC), 4700 **
Motorola Motorola, Inc. () was an American Multinational corporation, multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent p ...
M10800 family (1979), e.g. MC10800 ** Raytheon RP-16, a 16-bit processor consisting of seven integrated circuits, using four RALU chips and three CROM chips. * 8-bit slice: **
Four-Phase Systems Four-Phase Systems was a computer company, founded by Lee Boysel and others, which built one of the earliest computers using semiconductor main memory and MOS LSI logic. The company was incorporated in February 1969 and had moderate commercial ...
AL1 (1969, considered to be the first microprocessor used in a commercial product, now discontinued) ** Texas Instruments SN54AS888 / SN74AS888 ** Fairchild 100K ** ZMD (1978/1981), cascadable up to 32 bit * 16-bit slice: ** AMD
Am29100 Advanced Micro Devices (AMD) had a number of product lines with the part numbers beginning with "29". These families were generally not related to one another. The Am29(F, BL, DL, DS)xxx family contains a variety of Flash memory, flash memories, a ...
family ** Synopsys 49C402 **
ZFT Robotron VEB Kombinat Robotron (or simply Robotron) was the biggest East German electronics manufacturer. It was based in Dresden and employed 68,000 people (1989). It produced personal computers, SM EVM minicomputers, the ESER mainframe computers, sev ...
/ ZFTM Dresden (1979/1982), unreleased


Historical necessity

Bit slicing, although not called that at the time, was also used in computers before large-scale integrated circuits (LSI, the predecessor to today's
VLSI Very large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions or billions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit (Metal Oxide Semiconductor) c ...
, or very-large-scale integration circuits). The first bit-sliced machine was
EDSAC 2 EDSAC 2 was an early computer (operational in 1958), the successor to the Electronic Delay Storage Automatic Calculator (EDSAC). It was the first computer to have a microprogrammed control unit and a bit-slice hardware architecture. First cal ...
, built at the University of Cambridge Mathematical Laboratory in 1956–1958. Prior to the mid-1970s and late 1980s there was some debate over how much bus width was necessary in a given computer system to make it function. Silicon chip technology and parts were much more expensive than today. Using multiple simpler, and thus less expensive, ALUs was seen as a way to increase computing power in a cost-effective manner. While
32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32-bit units. Compared to smaller bit widths, 32-bit computers can perform large calculation ...
microprocessors were being discussed at the time, few were in production. The UNIVAC 1100 series mainframes (one of the oldest series, originating in the 1950s) has a
36-bit 36-bit computers were popular in the early mainframe computer era from the 1950s through the early 1970s. Starting in the 1960s, but especially the 1970s, the introduction of 7-bit ASCII and 8-bit EBCDIC led to the move to machines using 8-bit ...
architecture, and the 1100/60 introduced in 1979 used nine
Motorola MC10800 The Motorola MC10800 is a 4-bit bit-sliced processor designed by Motorola and introduced in 1979. It is implemented in ECL logic and is part of the M10800 family. A clone of the MC10800 was manufactured in the Soviet Union under the designation ...
4-bit ALU chips to implement the needed word width while using modern integrated circuits. At the time 16-bit processors were common but expensive, and 8-bit processors, such as the
Z80 The Z80 is an 8-bit microprocessor introduced by Zilog as the startup company's first product. The Z80 was conceived by Federico Faggin in late 1974 and developed by him and his 11 employees starting in early 1975. The first working samples were ...
, were widely used in the nascent home-computer market. Combining components to produce bit-slice products allowed engineers and students to create more powerful and complex computers at a more reasonable cost, using off-the-shelf components that could be custom-configured. The complexities of creating a new computer architecture were greatly reduced when the details of the ALU were already specified (and
debug In computer programming and software development, debugging is the process of finding and resolving '' bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems. Debugging tactics can involve int ...
ged). The main advantage was that bit slicing made it economically possible in smaller processors to use bipolar transistors, which switch much faster than NMOS or
CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...
transistors. This allowed much higher clock rates, where speed was needed for example, for
DSP DSP may refer to: Computing * Digital signal processing, the mathematical manipulation of an information signal * Digital signal processor, a microprocessor designed for digital signal processing * Yamaha DSP-1, a proprietary digital signal ...
functions or
matrix transformation In linear algebra, linear transformations can be represented by matrices Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fiction ...
or, as in the Xerox Alto, the combination of flexibility and speed, before discrete CPUs were able to deliver that.


Modern use


Software use on non-bit-slice hardware

In more recent times, the term bit slicing was reused by Matthew Kwan to refer to the technique of using a general-purpose CPU to implement multiple parallel simple
virtual machine In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardw ...
s using general logic instructions to perform single-instruction multiple-data ( SIMD) operations. This technique is also known as
SIMD within a register SIMD within a register (SWAR), also known by the name "packed SIMD" is a technique for performing parallel operations on data contained in a processor register. SIMD stands for ''single instruction, multiple data''. Flynn's 1972 taxonomy categorise ...
(SWAR). This was initially in reference to Eli Biham's 1997 article ''A Fast New DES Implementation in Software'', which achieved significant gains in performance of
DES Des is a masculine given name, mostly a short form (hypocorism) of Desmond. People named Des include: People * Des Buckingham, English football manager * Des Corcoran, (1928–2004), Australian politician * Des Dillon (disambiguation), sever ...
by using this method.


Bit-sliced quantum computers

To simplify the circuit structure and reduce the hardware cost of
quantum computer Quantum computing is a type of computation whose operations can harness the phenomena of quantum mechanics, such as superposition, interference, and entanglement. Devices that perform quantum computations are known as quantum computers. Though ...
s (proposed to run the MIPS32 instruction set) a 50 GHz superconducting "4-bit bit-slice arithmetic logic unit (ALU) for 32-bit rapid single-flux-quantum microprocessors was demonstrated".


See also

* Bit-serial architecture


References


External links

* a bitslicing primer presenting a pedagogical bitsliced implementation of the
Tiny Encryption Algorithm In cryptography, the Tiny Encryption Algorithm (TEA) is a block cipher notable for its simplicity of description and implementation, typically a few lines of code. It was designed by David Wheeler and Roger Needham of the Cambridge Computer Lab ...
(TEA), a
block cipher In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called ''blocks''. Block ciphers are specified cryptographic primitive, elementary components in the design of many cryptographic protocols and ...
{{Authority control Digital electronics Central processing unit University of Cambridge Computer Laboratory Bit-slice chips