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16-bit architecture
The HP BPC
HP 2100

The HP 2100 was a series of minicomputers produced by Hewlett-Packard from the mid 1960s to early 1990s. The 2100 was also a specific model in this series....
, introduced in 1975, was the world's first 16-bit microprocessor.

Prominent 16-bit processors include the PDP-11
PDP-11

The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s. Though not explicitly conceived as successor to DEC's PDP-8 computer in the Programmed Data Processor series of computers , the PDP-11 replaced the PDP-8 in many Real-time computing....
, Intel 8086
Intel 8086

The 8086 is a 16-bit microprocessor chip designed by Intel and introduced on the market in 1978, which gave rise to the x86 architecture. Intel 8088, released in 1979, was essentially the same chip, but with an external 8-bit bus , and is notable as the processor used in the original IBM PC....
, Intel 80286
Intel 80286

The Intel 286, introduced on February 1, 1982, was an x86 16-bit microprocessor with 134,000 transistors.It was widely used in IBM PC compatible computers during the mid 1980s to early 1990s....
 and the WDC 65C816. The Intel 8088
Intel 8088

The Intel 8088 is an Intel x86 microprocessor based on the Intel 8086, with 16-bit registers and an 8-bit external data bus. It can address up to 1 megabyte of random access memory....
 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16 bits long and arithmetic instructions, even though its external bus was 8 bits wide.

A 16-bit integer can store 216 (or 65536) unique values.






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16-bit architecture


The HP BPC
HP 2100

The HP 2100 was a series of minicomputers produced by Hewlett-Packard from the mid 1960s to early 1990s. The 2100 was also a specific model in this series....
, introduced in 1975, was the world's first 16-bit microprocessor.

Prominent 16-bit processors include the PDP-11
PDP-11

The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s. Though not explicitly conceived as successor to DEC's PDP-8 computer in the Programmed Data Processor series of computers , the PDP-11 replaced the PDP-8 in many Real-time computing....
, Intel 8086
Intel 8086

The 8086 is a 16-bit microprocessor chip designed by Intel and introduced on the market in 1978, which gave rise to the x86 architecture. Intel 8088, released in 1979, was essentially the same chip, but with an external 8-bit bus , and is notable as the processor used in the original IBM PC....
, Intel 80286
Intel 80286

The Intel 286, introduced on February 1, 1982, was an x86 16-bit microprocessor with 134,000 transistors.It was widely used in IBM PC compatible computers during the mid 1980s to early 1990s....
 and the WDC 65C816. The Intel 8088
Intel 8088

The Intel 8088 is an Intel x86 microprocessor based on the Intel 8086, with 16-bit registers and an 8-bit external data bus. It can address up to 1 megabyte of random access memory....
 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16 bits long and arithmetic instructions, even though its external bus was 8 bits wide.

A 16-bit integer can store 216 (or 65536) unique values. In an unsigned
Signedness

In computing, signedness is a property of variables representing numbers in computer programs. A numeric variable is signed if it can represent both negative and non-negative numbers, and unsigned if it can only represent positive numbers....
 representation, these values are the integers between 0
0 (number)

0 is both a number and the numerical digit used to represent that number in numeral system. It plays a central role in mathematics as the additive identity of the integers, real numbers, and many other algebraic structures....
 and 65535; using two's complement
Two's complement

The two's complement of a binary number is defined as the value obtained by subtracting the number from a large power of two .A two's-complement system or two's-complement arithmetic is a system in which negative numbers are represented by the two's complement of the absolute value; this system is the most common Signed number r...
, possible values range from -32768 to 32767. Hence, a processor with 16-bit memory address
Memory address

In computer science, a memory address is an identifier for a computer memory location, at which a computer program or a hardware device can store a piece of data and later retrieve it....
es can directly access 64 KiB of byte-addressable
Byte-addressable

Byte addressing refers to hardware architectures which support accessing individual bytes of data rather than only larger units called word orientation....
 memory.

16-bit processors have been almost entirely supplanted in the personal computer
Personal computer

A personal computer is any general-purpose computer whose original sales price, size, and capabilities make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator....
 industry, but remain in use in a wide variety of embedded applications. For example the 16-bit XAP processor
XAP processor

The XAP processor is a RISC central processing unit architecture developed by Cambridge Consultants Ltd since 1994. XAP processors are a family of 16-bit and 32-bit cores, all of which are intended for use in an application-specific integrated circuit or ASIC chip design....
 is used in many ASICs.

The 16/32-bit Motorola 68000
The Motorola 68000
Motorola 68000

The Motorola 68000 is a 16/32-bit Complex instruction set computer microprocessor core designed and marketed by Freescale Semiconductor ....
 is sometimes called "16-bit" because its data buses were 16 bits wide, however it was 32-bit
32-bit

The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295 or -2,147,483,648 through 2,147,483,647 using two's complement encoding....
 in that the general purpose registers were 32 bits long and most arithmetic instructions supported 32-bit arithmetic, with up to 16 megabytes of addressable RAM
Ram

Ram, ram, or RAM as a non-acronymic wordAs a non-acronymic word Ram, ram, or RAM may refer to:...
. Thus the 68000 software is 32-bit in nature, and forwards-compatible with other 32-bit processors. The 68000 processor of the Sega Mega Drive/Genesis
Sega Mega Drive

The is a History of video game consoles video game console released by Sega in Japan in 1988, North America in 1989, and the PAL region in 1990. Mega Drive was the name used in Japan and Europe, while it was sold under the name Sega Genesis in North America, as Sega was unable to secure legal rights to the Mega Drive name in that region....
 was a highly advertised feature of the video game system. Due to the saturation of this advertising, the 1988-1995 era of video game consoles is often called "the 16-bit era".

16-bit file format

A 16-bit file format is a binary
Binary file

A binary file is a computer file which may contain any type of data, encoded in Binary numeral system form for computer storage and processing purposes; for example, Document file format containing formatted text....
 file format
File format

A file format is a particular way to encode information for storage in a computer file.Since a disk drive, or indeed any computer storage, can store only bits, the computer must have some way of converting information to 0s and 1s and vice-versa....
 for which each data element is defined on 16 bits (or 2 Byte
Byte

A byte is a basic unit of measurement of Computer storage in computer science. In many computer architectures it is a Byte addressing memory address space....
s). An example of such a format is UTF-16 and the Windows Metafile Format
Windows Metafile

Windows Metafile is a on Microsoft Windows systems, originally designed in the early 1990s. Windows Metafiles are intended to be portable between applications and may contain both vector and bitmap components....
.

16-bit memory models

Similar to 64-bit
64-bit

64-bit CPUs have existed in supercomputers since the 1960s and in RISC-based computer workstation and Server s since the early 1990s. In 2003 they were introduced to the mainstream personal computer arena, in the form of the x86-64 and 64-bit PowerPC processor architectures....
's data models, the 16-bit Intel architecture allows for different memory models—ways to access a particular memory location. The reason for using a specific memory model is the size of the assembler instructions or required storage for pointers. Compilers of the 16-bit era generally had the following typewidth characteristic:

16-bit data model
Data model short int long pointers
IP16L32 (near) 16 16 32 16
I16LP32 (far) 16 16 32 32


“Tiny”
Code and data will be in the same segment (especially, the registers CS,DS,ES,SS will point to the same segment); “near” pointers are always used. Code, data
Heap

Heap may refer to:In computer science* heap , a tree-like data structure* The heap is the area of memory used for dynamic memory allocation...
 and stack together cannot exceed 64K.
“Small”
Code and data will be in different segments, and “near” pointers are always used. There will be 64K of space for code and 64K for data/stack.
“Medium”
Code pointers will use “far” pointers, enabling access to 1MB. Data pointers remain to be of the “near” type.
“Compact”
Data pointers will use “far” and code will use “near” pointers.
“Large”/“Huge”
Code and data pointers will be “far”.