Can all firms employ Just In Time stock systems?

No This is because some firms must have inventory at all times. For example, when you go to a Walmart, you expect that they will have most basic products in stock. So Walmart has to order this inventory in advance of demand. But a company like DELL, famous for its business model, can wait to build a computer until they have an order. However, DELL still keeps some inventory so that it can produce its computers in a timely manner. No one wants to want a month for a new computer. Very few companies that produce hard goods can use a true (100%) just in time business model. What has occurred is that many companies have used technology to reduce inventories, which reduces working capital.