is reduced and less power is needed to operate the cells. This, in turn, means that less electric current is needed for operation, and thus less time is needed to send the required amount of electrical charge into the system. In DRAM, in particular, the amount of charge that needs to be stored in a cell's capacitor also directly affects this time. As fabrication has improved, solid-state memory has improved dramatically in terms of performance. Modern DRAM chips had operational speeds on the order of 10 ns or less. A less obvious effect is that as density improves, the number of DIMMs needed to supply any particular amount of memory decreases, which in turn means less DIMMs overall in any particular computer. This often leads to improved performance as well, as there is less bus traffic. However, this effect is generally not linear. Effects on price Storage density also has a strong effect on the price of memory, although in this case, the reasons are not so obvious. In the case of disk-based media, the primary cost is the moving parts inside the drive. This sets a fixed lower limit, which is why the average selling price for both of the major HDD manufacturers has been US$45–75 since 2007. That said, the price of high-capacity drives has fallen rapidly, and this is indeed an effect of density. The highest capacity drives use more platters, essentially individual hard drives within the case. As the density increases, the number of platters can be reduced, leading to lower costs. Hard drives are often measured in terms of cost per bit. For example, the first commercial hard drive, IBM's RAMAC in 1957, supplied 3.75 MB for $34,500, or $9,200 per megabyte. In 1989, a 40 MB hard drive cost $1200, or $30/MB. And in 2018, 4 Tb drives sold for $75, or 1.9¢/GB, an improvement of 1.5 million since 1989 and 520 million since the RAMAC. This is without adjusting for inflation, which increased prices nine-fold from 1956 to 2018. Solid-state storage has seen a similar drop in cost per bit. In this case the cost is determined by the yield, the number of viable chips produced in a unit time. Chips are produced in batches printed on the surface of a single large silicon wafer, which is cut up and non-working samples are discarded. Fabrication has improved yields over time by using larger