Access time is the amount of time that passes between a request for data and when the data is provided. There are many other terms that refer to access time such as memory latency and seek time. These terms are different for various mediums.
One of the most common types of access time referred to is memory latency. This refers to the amount of time it takes for a memory controller to access and prepare an area of memory for output. This is an extremely important type of latency since it is often the determining factor in how fast programs may run on a system.
Another well-known type of access time is referred to as network latency. This type of latency refers to the amount of time required for a packet of information to travel from one point in a network to another. In terms of Internet access, this time can vary significantly depending on where the packet is being sent. For example, the network latency of sending a packet to a computer on the same physical network may be 15 milliseconds, while it may be several seconds when sent to a computer located in a distant country.
Hard drives and optical disk drives have several different types of latency. The first is known as rotational delay. Both hard drives and optical disk drives spin. The rotational delay is the time required for the disk to spin into a position where the read/write head can access the data.
The second type of latency in these types of systems is known as seek time. Once the disk has spun to the correct position, the read/write head must then move into the correct position for reading the data. The time these two processes take is variable and depends on how far from the original position the new position is located.
The final type of latency is known as the transfer time. This is how long the process of transferring information off the drive takes. This access time is different for various types of drives and is referred to as the bit rate.
With many variables tied to the latency of hard drives and optical disk drives, it can be difficult to determine the actual access time for a given drive. Drives are often advertised by their fastest speeds. This count often solely refers to the bit rate of the drive.