Solid-state-disks(SSDs) holding up to 256Gbyte could be in mainstream notebooks within three years, according to flash memory vendor Sandisk.

By that time an estimated one in five new laptops will have an SSD instead of a hard disk, said Doreet Oren, product-marketing director in the company's computer solutions division.

Sandisk is selling 32Gbyte and 64Gbyte laptop SSDs in 1.8in and 2.5in formats but both the size and the capacity are dictated by the market rather than the technology.

SSDs have been used by the military for a decade but only in the past year have memory prices fallen enough to put them within reach of the business and consumer markers.

Oren said the "sweet spot" came when SSDs holding 32Gbytes, considered to be ample storage for the average laptop user, became affordable. Multi-level-cell (MLC) memory, which stores several bits per cell by using more than one voltage, as well as competition is likely to drive prices down further.

The Sandisk SSDs are currently being sold only to laptop vendors, who want slot-in replacements for 1.8in and 2.5in hard disks. Dell offers four models using SSDs from Sandisk, though Oren could not say whether it is the only supplier.

She believes other formats will appear as SSDs cease to be simply hard-disk replacements and become installed in different classes of device.