8-bit

In computer architecture, 8-bit integers, memory addresses, or other data units are those that are 8 bits (1 octet) wide. Also, 8-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 8-bit is also a generation of microcomputers in which 8-bit microprocessors were the norm.

The IBM System/360 introduced byte-addressable memory with 8-bit bytes, as opposed to bit-addressable or decimal digit-addressable or word-addressable memory, although its general purpose registers were 32 bits wide, and addresses were contained in the lower 24 bits of those addresses. Different models of System/360 had different internal data path widths; the IBM System/360 Model 30 (1965) implemented the 32-bit System/360 architecture, but had an 8 bit native path width, and performed 32-bit arithmetic 8 bits at a time.^[1]

The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system; it had 8-bit data words and 16-bit addresses. The Zilog Z80 (compatible with the 8080) and the Motorola 6800 were also used in similar computers. The Z80 and the MOS Technology 6502 8-bit CPUs were widely used in home computers and second- and third-generation game consoles of the 1970s and 1980s. Many 8-bit CPUs or microcontrollers are the basis of today's ubiquitous embedded systems.

Details

There are 2⁸ (256) different possible values for 8 bits. When unsigned, it has possible values ranging from 0 to 255, when signed, it has -128 to 127.

Eight-bit CPUs use an 8-bit data bus and can therefore access 8 bits of data in a single machine instruction. The address bus is typically a double octet wide (i.e. 16-bit), due to practical and economical considerations. This implies a direct address space of only 64 KB on most 8-bit processors.

Notable 8-bit CPUs

The first commercial 8-bit processor was the Intel 8008 (1972) which was originally intended for the Datapoint 2200 intelligent terminal. Most competitors to Intel started off with such character oriented 8-bit microprocessors. Modernized variants of these 8-bit machines are still one of the most common types of processor in embedded systems.

Another notable 8-bit CPU is the MOS Technology 6502; it, and variants of it, were used in a number of personal computers such as the Apple I and Apple II, the Atari 8-bit family, the BBC Micro, and the Commodore PET and Commodore VIC-20, and in a number of video game consoles such as the Atari 2600 and the Nintendo Entertainment System.

Early or popular 8-bit processors (incomplete)
Manufacturer	Processor	Year	Comment
Intel	8008	1972	Datapoint 2200 compatible
Signetics	2650	1973
Intel	8080	1974	8008 source compatible
Motorola	6800	1974
Fairchild	F8	1975
MOS	6502	1975	Similar to 6800, but incompatible
Microchip	PIC	1975	Harvard architecture microcontroller
RCA	1802	1976
Zilog	Z80	1976	8080 binary compatible
Intel	8085	1977	8080 binary compatible
Motorola	6809	1978	6800 source compatible
Zilog	Z8	1978	Harvard architecture microcontroller
Intel	8051	1980	Harvard architecture microcontroller
MOS	6510	1982	Enhanced 6502 custom-made for use in the Commodore 64
Ricoh	2A03	1982	6502 clone minus BCD instructions for the Nintendo Entertainment System
Zilog	Z180	1985	Z80 binary compatible
Motorola	68HC11	1985
Atmel	AVR	1996
Zilog	EZ80	1999	Z80 binary compatible
Infineon	XC800	2005
Freescale	68HC08
Hudson	HuC6280
Motorola	6803
NEC	78K0^[2]

References

↑ Amdahl, G. M.; Blaauw, G. A.; Brooks, F. P. (1964). "Architecture of the IBM System/360". IBM Journal of Research and Development. 8 (2): 87–101. doi:10.1147/rd.82.0087.
↑ NEC 78K0

CPU technologies
Architecture	Turing machine Post–Turing machine Universal Turing machine Quantum Turing machine Belt machine Stack machine Register machine Counter machine Pointer machine Random access machine Random access stored program machine Finite-state machine Queue automaton Von Neumann Harvard (Modified) Dataflow TTA Cellular Artificial neural network Machine learning Deep learning Neural processing unit (NPU) Convolutional neural network Load/store architecture Register memory architecture Register register architecture Endianness FIFO Zero-copy NUMA HUMA HSA Heterogeneous computing Parallel computing Amorphous computing Reconfigurable computing Cognitive computing DNA computing Peptide computing Chemical computing Organic computing Wetware computer Quantum computing Neuromorphic computing Optical computing Reversible computing Unconventional computing Hypercomputation Ternary computer Symmetric multiprocessing (SMP) Asymmetric multiprocessing (AMP) Cache hierarchy Memory hierarchy
ISA types	ASIP CISC RISC EDGE (TRIPS) VLIW (EPIC) MISC OISC NISC ZISC Comparison
ISAs	x86 z/Architecture ARM MIPS Power Architecture (PowerPC) SPARC VISC Mill Itanium (IA-64) Alpha Prism SuperH Clipper VAX Unicore PA-RISC MicroBlaze
Word size	1-bit 2-bit 4-bit 8-bit 9-bit 10-bit 12-bit 15-bit 16-bit 18-bit 22-bit 24-bit 25-bit 26-bit 27-bit 31-bit 32-bit 33-bit 34-bit 36-bit 39-bit 40-bit 48-bit 50-bit 60-bit 64-bit 128-bit 256-bit 512-bit Variable
Execution	Instruction pipelining Bubble Operand forwarding Out-of-order execution Register renaming Speculative execution Branch predictor Memory dependence prediction Hazards
Parallel level	Bit Bit-serial Word Instruction Pipelining Scalar Superscalar Task Thread Process Data Vector Memory
Multithreading	Temporal Simultaneous (SMT) (Hyper-threading) Speculative (SpMT) Preemptive Cooperative Clustered Multi-Thread (CMT) Hardware scout
Flynn's taxonomy	SISD SIMD (SWAR) SIMT MISD MIMD SPMD Addressing mode
CPU performance	Instructions per second (IPS) Instructions per clock (IPC) Cycles per instruction (CPI) Floating-point operations per second (FLOPS) Transactions per second (TPS) SUPS Performance per watt Orders of magnitude (computing) Cache performance measurement and metric
Core count	Single-core processor Multi-core processor Manycore processor
Types	Central processing unit (CPU) GPGPU AI accelerator Vision processing unit (VPU) Vector processor Barrel processor Stream processor Digital signal processor (DSP) I/O processor/DMA controller Network processor Baseband processor Physics processing unit (PPU) Coprocessor Secure cryptoprocessor ASIC FPGA FPOA CPLD Microcontroller Microprocessor Mobile processor Notebook processor Ultra-low-voltage processor Multi-core processor Manycore processor Tile processor Multi-chip module (MCM) Chip stack multi-chip modules System on a chip (SoC) Network on a chip (NoC) Multiprocessor system-on-chip (MPSoC) Programmable System-on-Chip (PSoC)
Components	Execution unit (EU) Arithmetic logic unit (ALU) Address generation unit (AGU) Floating-point unit (FPU) Load-store unit (LSU) Fixed-point unit (FXU) Vector unit (VU) Branch predictor Branch execution unit (BEU) Instruction Decoder Instruction Scheduler Instruction Fetch Unit Instruction Dispatch Unit Instruction Sequencing Unit Unified Reservation Station Barrel shifter Uncore Sum addressed decoder (SAD) Front-side bus Back-side bus Northbridge (computing) Southbridge (computing) Adder (electronics) Binary multiplier Binary decoder Address decoder Multiplexer Demultiplexer Registers Cache Memory management unit (MMU) Input–output memory management unit (IOMMU) Integrated Memory Controller (IMC) Power Management Unit (PMU) Translation lookaside buffer (TLB) Stack engine Register file Processor register Hardware register Memory buffer register (MBR) Program counter Microcode ROM Datapath Control unit Instruction unit Re-order buffer Data buffer Write buffer Coprocessor Electronic switch Electronic circuit Integrated circuit Three-dimensional integrated circuit Boolean circuit Digital circuit Analog circuit Mixed-signal integrated circuit Power management integrated circuit Quantum circuit Logic gate Combinational logic Sequential logic Emitter-coupled logic (ECL) Transistor–transistor logic (TTL) Glue logic Quantum gate Gate array Counter (digital) Bus (computing) Semiconductor device Clock rate CPU multiplier Vision chip Memristor
Power management	APM ACPI Dynamic frequency scaling Dynamic voltage scaling Clock gating
Hardware security	Non-executable memory (NX bit) Bounds checking (Intel MPX) Intel Secure Key Hardware restriction (firmware) Software Guard Extensions (Intel SGX) Trusted Execution Technology OmniShield Trusted Platform Module (TPM) Secure cryptoprocessor Hardware security module Hengzhi chip
Related	History of general-purpose CPUs

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.

8-bit

Details

Notable 8-bit CPUs

See also

References