Click above to get retro games delivered to your door ever month!

  The data bus works with the address bus to carry data throughout the
  computer. The PC's 8088-based system uses a data bus that has 8 signal
  lines, each of which carries a single binary digit (bit); data is
  transmitted across this 8-line bus in 8-bit (1-byte) units. The 80286
  microprocessor of the AT uses a 16-bit data bus and therefore passes
  data in 16-bit (1-word) units.

  The 8088, being a 16-bit microprocessor, can work with 16 bits of data
  at a time, exactly like its relative the 80286. Although the 8088 can
  work with 16-bit numbers internally, the size of its data bus allows the
  8088 to pass data only 8 bits at a time. This has led some people to
  comment that the 8088 is not a true 16-bit microprocessor. Rest assured
  that it is, even though it is less powerful than the 80286. The 16-bit
  data bus of the 80286 does help it move data around more efficiently
  than the 8088, but the real difference in speed between the 8088 and the
  AT comes from the AT's faster clock rate and its more powerful internal
  organization.

  There is an important practical reason why so many computers, including
  the older members of the PC family, use the 8088 with its 8-bit data
  bus, rather than the 8086 with its 16-bit bus. The reason is simple
  economics. A variety of 8-bit circuitry elements are available in large
  quantities at low prices. When the PC was being designed, 16-bit
  circuitry was more expensive and was less readily available. The use of
  the 8088, rather than the 8086, was important not only to hold down the
  cost of the PC, but also to avoid a shortage of parts. The price of
  16-bit circuitry elements has decreased significantly since then,
  however, and it has become economically feasible to use the more
  efficient 80286 with its 16-bit bus. Furthermore, the 80286 is able to
  use a mixture of 8-bit parts and 16-bit parts, thereby maintaining
  compatibility within the PC family.